The present invention relates to an improved appendage processing assembly for making photoemissive cathodes in imaging devices such as silicon intensifier tubes, intensified charge-coupled image sensors, image intensifier tubes and photomultiplier tubes.
U.S. Pat. No. 2,744,808, issued to Ruedy on May 8, 1956, discloses an apparatus for use in evaporating chemical materials, specifically the constituents of a photoemissive cathode, including antimony and one or more alkali metals onto a faceplate within an evacuated tube envelope. The apparatus utilizes a unidirectional antimony source and an alkali chamber having a small opening near one end. The structure is complex and expensive to manufacture. Furthermore, while the antimony source is disclosed to be unidirectional, no structure is disclosed for restricting the deposition of antimony to only the faceplate of the tube envelope.
U.S. Pat. No. 3,535,011, issued to Matheson et al. on Oct. 20, 1970, discloses a photomultiplier tube which utilizes two chambers for making the photoemissive cathode. Alkali materials are provided in one chamber, and antimony is slidably disposed in a second chamber. No structure is disclosed for restricting the direction of the antimony evaporation or for centering the antimony source within the tube envelope during the antimony evaporation step. The two chamber structure also is unnecessarily complex and expensive.
U.S. Pat. No. 4,396,853, issued to Caraher on Aug. 2, 1983, discloses an evaporator housing which contains an antimony boat. The boat is mounted on a pair of coaxial rods which are attached to a transversely disposed plate having apertures therein for sliding on a second pair of rails which extend along the evaporator housing. No structure is disclosed to prevent the deposition of antimony on portions of the tube not associated with the photoemissive cathode. Additionally, the alkali generators are located within the tube where they can create particles. The slider structure also has another problem in that it is difficult to overcome the friction associated with the apertured plate sliding on a pair of rods.
A need therefore exists for a single appendage that contains both the antimony and the alkali materials in a single, reliable structure that is easy to assemble, has minimun sliding friction and which properly positions the antimony evaporator within the envelope and limits the antimony deposition only to the photocathode surface.